Tube heater



y 1968 K. w. FLEISCHER 3,385,271

TUBE HEATER Filed Jan. 31, 1967 INVENTOR. KURT W. FLEISCHER ATTORNEY.

United States Patent 3,385,271 TUBE HEATER Kurt W. Fleischer, Ambler, Pan, assignor to Selas Corporation of America, a corporation of Pennsylvania Filed Jan. 31, 1967, Ser. No. 612,948 '7 Claims. (Cl. 122-510) ABSTRACT OF THE DISCLOSURE The vertically extending passes of a tube coil are supported by the return bends at their upper ends. Each return bend is provided with a bracket through which a roller extends with the roller resting upon horizontal beams above the furnace chamber. Burners in the furnace chamber walls are placed to supply heat evenly throughout the length of each coil pass.

Background of the invention 1 In one type of tube heater used in the petrochemical industry there is provided an elongated tube in the form of a serpentine coil. As heat is applied to the coil, and the fluid flowing therethrough increases in temperature, the coil expands with some parts expanding more than others. This condition has created warped coils and, in some cases, the coils have cracked at the welds. In any event, expansion of the coils is a serious problem in the design of any tube heater.

Summary of the invention According to the invention, a tube heating furnace is provided with a serpentine coil having vertically extending tube passes. The upper return bend between each tube length or pass is located above the furnace chamber, and is provided with a bracket. A roller extends through each bracket and rests on supporting beams in such a way that the coil is supported, but each convolution can move slightly so that stresses in the tube lengths are reduced. The burners in the furnace are so positioned with respect to the coil that the individual passes are evenly heated, and a desired temperature gradient can be obtained from one end to the other of the coil.

It is an object of the invention to provide an improved support for the coil in a tube heater. It is a further object of the invention to provide the placement of burners in a tube heater so that the tubes will be heated evenly from end to end, if desired, and evenly around their circumference.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a section view through the furnace taken on line 11 of FIG. 2;

FIG. 2 is a sectional plan view of the furnace showing the placement of the coil with respect to the burners and taken on line 22 of FIG. 1;

FIG. 3 is an enlarged view in section showing the support for the upper ends of the coil convolutions;

FIG. 4 is a section taken on line 4-4 of FIG. 3; and

FIG. 5 is an enlarged view of the upper end of one of the return bends taken from the side in FIG. 3.

Detailed description Referring particularly to FIGS. 1 and 2 of the drawing, there is shown a tube heater constructed in accordance 3,385,271 Patented May 28, 1968 with ordinary furnace practice which heater has a furnace chamber that is surrounded by side walls 1 and 2 and end walls 3 and 4. The walls are joined at their lower ends by a floor 5 and at their upper ends by a roof 6. At one section of the roof there is provided a stack 7 through which the products of combustion are exhausted.

Each of side walls 1 and 2 has in it a plurality of vertically extending rows of burners 8, preferably of the radiant cup type, with each row of burners being supplied with fuel through a vertically extending manifold 9. Each row of burners is supplied through an individual manifold so that the rows may be controlled separately. There are also provided valves 11 in the manifold for each burner and each manifold has a valve 12 which controls the supply of fuel to that particular row.

Located in the furnace chamber is a continuous serpentine fluid heating coil 13 which is comprised of a plurality of vertically extending tube passes 14 joined by upper return bends 15 and lower return bends 16. The upper return bends extend through a slot 17 which is formed lengthwise in roof 6 so that the bends themselves are not in the hot portion of the furnace chamber. The coil is supported from the upper return bends on a pair of horizontally extending channel irons 18 which are attached to the framework of the furnace. To this end, each return bend 15 has Welded to it a bracket 19 having a hole 21 in it. A roller 22 extends through each of the brackets and rests on the upper flange of channels 18. A cover 23 may be provided over the rollers and the slot 17 in the furnace chamber. In order to close the slot and the upper part of the furnace chamber there are provided a plurality of refractory bricks 24, each of which has a half-circle cut out of it so that they surround the vertically extending tube pass 14 where it passes through the roof. It will be noted that the pairs of bricks 24 surrounding each tube are separated by a space 25 for a purpose to be described. It is preferred that the space around the upper return bends between the channels 18 and above bricks 24 be filled with a fibrous insulating material in order to seal the upper end of the chamber. Such material will not fall through the spaces 25 and can easily be removed when it is necessary to repair the return bends or remove the coil.

The lower ends of each pair of tube passes, which are joined by return bends 16 are guided, in their expanding movement as the furnace is heated, by means of a pin 26 that is welded to each of these return bends, with each pin extending downwardly into a closed-end socket 27 in the floor 5. The size of the socket is only slightly larger than the size of the pin and its lower end is closed so that there will be no chance for air to infiltrate through these openings into the heater chamber.

In constructing the furnace, the walls including the burners, are built with the slot 17 remaining open. The entire coil 13 is then lowered through slot 17 by a suitable crane. While the coil is being lowered into position, rollers 22 are inserted through the openings in brackets 19. When the lowering is finished, rollers 22 will rest on beams 18. Any required type of coil can be used in the furnace. The coil can have all its passes in a single horizontal row if it is so desired. The coil shown in the drawings, however, has alternate passes offset with respect to each other to form a zig-zag line in FIG. 2 This, in effect, makes two parallel rows of tubes in the furnace. An advantage of this construction is that a longer coil can be used in a furnace of a given size than would be possible if the various passes were in a single row. In connection with a coil of the type shown, it will be noted that the coil is so located lengthwise of the furnace between ends 3 and 4 that alternate vertically extending tube passes are axially aligned with respect to a row of burners on the side of the furnace remote therefrom, whereas the tube passes in the row adjacent a particular furnace side, are not aligned with rows of burners on that side. With this particular relative placement of tubes ad burners, a more even heat can be imparted to all of the tubes and around the circumference thereof than would be possible if the tube pass on the side of a burner was directly in line with the burner axis. It is noted that the end of tube in which the fluid being heated is supplied and the end form which the heated fluid is withdrawn, are fixed in a suitable and conventional manner in the upper portion of the furnace so that the supply and discharge pipes can be connected to them. It is also noted that a preheating or convection coil (not shown) can be placed in a conventional manner in stack 17 to be connected to the inlet end of the coil.

When the furnace is in operation, one end of the coil will normally be cooler than the other because the cool fluid is introduced in the one end. Furthermore, there will be differential expansion between the various tube passes as they are heated. This expansion and making provision for it, is a serious problem in every furnace of this type. The manner in which the coil is placed in the furnace in accordance with this invention, overcomes many, if not all, of the prior problems. The lower ends of the coils are guided by pin 26 and can expand and contract lengthwise as necessary. Some slight lateral movement can also be provided, depending upon the relative size of pin 26 and sockets 27. The upper ends of the tube at each return bend, can move slightly with respect to each other since each end is mounted individually. The provision of rollers 22, which can roll along channels 18, permits the individual loops of the coil to shift slightly as is necessary in order to prevent undue strains on the various passes of the coil if the outlet end, for example, is heated more than the inlet end. The spaces 25 between the bricks 24 permit the shifting without imposing any strain upon the furnace or upon the coil itself.

With the present construction it is possible to heat each vertical loop of the coil by adjusting the fuel supply in separate manifolds to supply the amount of heat needed individually, independently of the heat needed by an adjacent group of tubes so that a desired gradient of heating can be obtained upon the fluid being heated as it fiows from one end of the coil to the other. Also, the upper burners of a row can be fired at a different rate from the lower burners to compensate for the heating effect of rising combustion gases. The mounting of the tubes permits them to expand and contract as required so that there is no possibility of the tube cracking due to the strain.

While in acordance with the provisions of the Statutes I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certain features of my invention may be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a tube heater, structure forming a vertically extending furnace chamber having sidewalls, a floor and a roof, said roof being provided with a slot extending lengthwise thereof, a plurality of vertically extending rows of burners in said side walls, a vertically disposed serpentine tube coil in said chamber between said side walls, the vertical passes of said coil being joined by upper and lower return bends, the upper return bends extending through said slot, a bracket attached to each upper return bend, means cooperating with said brackets to support individually said upper return bends on said roof, said means including means to permit said upper return bends to move independently of each other and relative to said roof, and means cooperating with said lower return bends to guide said tube passes as they expand lengthwise.

2. The combination of claim 1 in which a beam extends along said roof at each side of said slot, a bracket having an opening therein is fastened to each upper return bend, and a roller extending through each opening, said rollers resting on said beams.

3. The combination of claim 1 in which each lower return bend has a pin fastened to and projecting downwardly therefrom, and means in said floor to receive and guide each pin as said tube passes expand.

4. The combination of claim 2 including a plurality of blocks formed to surround the passes of said tube coil, and means to mount said blocks around said tube passes in said slot in said roof, some of said blocks being spaced from each other.

5. The combination of claim 4 in which the space formed between said beams and above said blocks around the upper return bends is filled with insulating material.

6. The combination of claim 1 in which the tube passes of said coil are offset with respect to each other to form in plan a zig-zag line, and said rows of burners are so located with respect to said tube passes that a tube pass is axially in front of the burners of each row, with said tube pass being adjacent to the side of the furnace opposite that containing the row of burners with which it is aligned.

7. The combination of claim 6 in which each vertical row of burners is supplied with fuel from an individual manifold, a valve between the manifold and each burner to control the supply of fuel to each burner, and a valve to control the fuel to each manifold.

References Cited UNITED STATES PATENTS 2,825,313 3/1958 Born et al l22356 3,182,638 5/1965 Lee et al 122-356 XR 3,240,204 3/1966 Wiesenthal 122-356 XR KENNETH W. SPRAGUE, Pliflldl) Examiner. 

